I use fragrance-free dryer sheets to clean off any fusible (new ones because it's the fabric softener that loosens up the fusible). I can usually remove the starch with just a wet washcloth while the iron is still warm (need to fold it a number of times so your fingers don't get too close to the hot sole plate). My current iron has an anti-calc feature to prevent white calcium build-up in the steam holes & also has a self-clean button. On my previous iron, I used Whink Steam Iron Cleaner.
I'm trying to be better about caring for my irons by using parchment paper or a pressing cloth to keep the fusible from getting on my iron. I also now usually let the spray starch seep into the fabric for a bit before ironing/pressing (and yes, I usually spray starch one side & iron the other side -- if it needs more starch, once I've finished one side, I'll repeat on the reverse).